CN106330342B - A kind of underwater sound communication Doppler factor estimation method of low computation complexity - Google Patents
A kind of underwater sound communication Doppler factor estimation method of low computation complexity Download PDFInfo
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Abstract
A kind of Doppler factor estimation method of low computation complexity, is related to underwater sound communication.A kind of transmission packet structure is devised, i.e., is inserted into LFM signal, protection interval and pure-tone pulse (CW) signal before data to be sent.The present invention is divided into two steps to Doppler factor estimation, uses FFT frequency measuring method to CW signal first, Doppler factor is locked in a smaller range；LFM signal accurately estimates Doppler factor using ambiguity function method again.The quantity of correlator is the estimated accuracy of the Doppler factor range and Doppler factor searched for by needs to determine in ambiguity function method, search range is the Doppler factor range that the first step determines in the present invention, therefore search range is substantially reduced, it is only necessary to a small amount of correlator.The present invention utilizes the characteristics of CW signal and LFM signal, and under the premise of ensuring that the absolute value of evaluated error is less than or equal to estimated accuracy, computation complexity is greatly decreased, and easy to accomplish.
Description
[technical field]
The present invention relates to underwater sound communications, more particularly to are estimated based on FFT frequency measuring method and being combined based on ambiguity function method
The underwater sound communication Doppler factor estimation method of meter.
[background technique]
Underwater sound communication not only has great application value in military field, it was in civil field application valence in recent years
It is worth more and more prominent, such as multi-sensor, early warning of marine disasters and search and rescue, resource exploration.Current China underwater sound communication skill
Art is also in a starting stage, mainly applies transmission rate is lower and the occasion of movement speed very little, this is because
The development of underwater sound communication system receives the very big limitation of underwater acoustic channel condition, compared with other communication channels, underwater acoustic channel table
Reveal the stochastic behaviour that complicated time-varying, space-variant, frequency become.Especially the propagation rate of sound wave in water is low (1500m/s), causes
It is with serious multipath effect and Doppler effect, in addition the complexity that underwater acoustic channel is intrinsic, such as ambient noise are strong all
More characteristics restrict effective progress of underwater sound communication, become develop in numerous research fields of wireless communication it is most slow.With
Ocean development it is movable frequently, people have more expectations to mobile and high speed underwater acoustic communication systems, and whether high speed is also
The problem of being mobile underwater sound communication system, all having to face is Doppler shift.Due to the propagation of sound wave in water
Rate only has 1500m/s, when the transmitting-receiving both ends of communication system are there are when relative motion, receive in signal and has serious Doppler
Effect, though without relative motion, the fluctuating etc. from time-varying sea be also possible to cause more serious Doppler effect and
Random phase rises and falls, so that communication system performance sharply declines, so effective Doppler shift technology is water
A research emphasis in sound communication system.
The estimation method in underwater sound communication is mostly to be based on ambiguity function at present, and there are two types of main ways of realization, and one
To ask related to received signal using one group of correlator for correlator estimation method, the range that this Doppler estimates with
Precision determines the quantity of required correlator.If the range of Doppler frequency shift is ± 1%, estimation accuracy is 0.02%, then
Need 100 independent correlators.Obvious the method calculates greatly, is unfavorable for the occasion for requiring real-time high；Two be block Doppler
Estimation method sends each insertion LFM signal before and after data really, does phase with signal is received with known linear FM signal
It closes, the length of reception signal is measured with the peak value of head and the tail, be somebody's turn to do by the way that the length for comparing transmitting signal with receiving signal is available
The Doppler factor of frame signal, the method will appear under practical underwater acoustic channel, correlation peak decline, relevant peaks division etc. are existing
As.Doppler factor estimation method in underwater sound communication based on FFT frequency measuring method also has a wide range of applications, this method meter
Calculation amount is smaller, strong real-time, and detection accuracy is limited by CW signal duration and transformation points, simple effective by increasing
Data are counted to improve frequency detection accuracy (i.e. duration), and the complexity of operation is on the one hand increased, it is often more important that,
In practical application, secured transmission of payload data points are cannot arbitrarily to increase, therefore this method is extremely difficult to ideal precision.
[summary of the invention]
In view of this, it is necessary to provide a kind of low computation complexity and the underwater sound Doppler factor estimation sides of degree of precision
Method.It is an object of the invention to provide a kind of low computation complexity and with degree of precision underwater sound Doppler factor estimation method,
This method is to transmit packet structure based on underwater sound communication system and realize, the packet structure that the present invention designs is believed by LFM
Number, protection interval, CW signal, protection interval, data to be transmitted successively form.The method includes:
The just range estimation of step 1) Doppler factor；
Step 2) Doppler factor is accurately estimated.
Step 1) is that Doppler factor is locked in a smaller range, and the step is specific as follows:
1) CW signal initial position is determined by packet structure, extracts subsequent CW signal；
2) frequency detecting is carried out to CW signal using traditional FFT frequency measuring method, after carrying out FFT transform, searches for wherein amplitude
Point N corresponding to maximum1, calculate respective frequencies fmax, it is assumed that CW signal frequency is f when transmittingcw, available Doppler factor
Δ=fmax/fcw-1.Due to fence effect, acquired frequency fmaxIt may be with the frequency f' of CW signal when receivingcwHave certain inclined
Difference, so Doppler factor Δ may have relatively large deviation with true Doppler factor.In order to avoid such case, first comparison point
N1Left and right two o'clock amplitude size show that the biggish point of amplitude is N2；
3) according to FFT transform points N and point N1And N2Positional relationship and sample frequency fsTo determine Doppler factor
First range delta, such as fruit dot N2In point N1When the right, then Doppler factor just range can be obtained are as follows:
fmax/fcw-1≤Δ≤(fmax+fs/N/2)/fcw-1
As point N2In point N1When the left side, then Doppler factor just range can be obtained are as follows:
(fmax-fs/N/2)/fcw-1≤Δ≤fmax/fcw-1。
The matched filter of the determination CW signal initial position specific method of above-mentioned progress LFM signal in transmission data packet
Matched filtering is carried out to received data packet, it may be determined that CW signal initial position.
Step 2) obtains Doppler factor and accurately estimates, which estimated by ambiguity function method,
The LFM signal that will be received passes through a series of corresponding LFM signal correlator (matched filter) of different Doppler factors, when
When the shock response of correlator and input signal match, the output signal-to-noise ratio of correlator is maximum, this correlator shock response institute
Corresponding Doppler factor is necessarily able to reflect the size of the Doppler factor of input signal, specific as follows:
1) the quantity M of correlator is determined, wherein the first model of Doppler factor obtained by the quantity M Shi Gen Ju Walk rapid 1 of correlator
Enclose the estimated accuracy Δ of Δ and Doppler factormaxIt determines, i.e. M=[(f2/fcw-f1/fcw)/Δmax], wherein [] indicates big
In equal to (f2/fcw-f1/fcw)/ΔmaxSmallest positive integral；
2) the corresponding LFM Signal Matching filter of M difference Doppler factor is set, and the resolution ratio of matched filter group is
Δmax, the LFM signal received is passed through into matched filter group；
3) maximum value for comparing the output of M matched filter, obtains maximum value, correlator corresponding to maximum value be exactly with
The received LFM signal correlation of institute is best, to obtain accurate Doppler factor.
Compared with prior art, the invention has the following outstanding advantages:
1) with traditional FFT estimate frequency compared with, which obviate by increase CW signal duration come
Increase estimated accuracy, and operand does not increase significantly；
2) compared with relevant Doppler estimation method, in the requirement for not reducing Doppler factor estimated accuracy
Under, operand is greatly decreased；
3) data frame structure is simple, realizes the features such as simple, arithmetic accuracy is high, strong real-time is easily achieved.
[Detailed description of the invention]
Fig. 1 is that packet structure is transmitted in transmission designed by the present invention；
Fig. 2 is LFM signal when delay is 0, the sectional drawing of ambiguity function figure；
Fig. 3 is when underwater sound communication Doppler factor is 0.01, and LFM signal passes through a series of different Doppler factor phases
When corresponding LFM correlator (i.e. matched filter) is organized, the maximum value of each matched filter output；
Fig. 4 is the correlation method figure of the accurate estimating Doppler factor of the present invention；
Fig. 5 is that Doppler factor of the present invention estimates process flow diagram；
[specific embodiment]
It is illustrated below in conjunction with specific embodiment and attached drawing.
1, the underwater sound transmits packet structure
The design for transmitting packet structure is most important, from preliminary Doppler factor range to being accurate to a certain precision
Doppler factor realizes on its basis, and attached drawing 1 is that the designed underwater sound of the invention transmits data packet, in pack arrangement
LFM signal is used to determine CW signal starting position and is used to the accurate estimating Doppler factor, due to the relative time delay of underwater acoustic channel
Larger, protection interval takes 40ms in the present invention.
1) LFM signal LFM signal (also referred to as Chirp signal), mathematic(al) representation are as follows:
F in formula0For center frequency,For rectangular signal, i.e.,
Wherein K=B/T, is chirp rate, and B is LFM signal bandwidth.
The matched filter of LFM signal, it is known that the time-domain pulse response of the matched filter of signal s (t) are as follows:
H (t)=s*(t0-t) (3)
t0It is to make filter physics that can realize attached time delay.When theory analysis, t can be enabled0=0,3 formulas are rewritten,
H (t)=s*(-t) (4)
1 formula is substituted into the impulse response that 4 formulas obtain the matched filter of LFM signal are as follows:
LFM signal start frequency is 10KHz, cutoff frequency 20KHz, duration 40ms in the present invention.
S (t) obtains output signal s by system h (t)o(t),
By (7) it is found that its absolute value is Xin Ke (s inc) function after LFM signal passes through matched filtering.
2, the estimation of the first range of Doppler factor
Range at the beginning of carrying out Doppler factor with the CW signal in data frame in the present invention is estimated, i.e., locks Doppler factor
It is scheduled on a lesser range.The frequency of CW signal is set in the present invention as fcw=10KHz, y (t)=A0cos(2πfcwT), it holds
The continuous time is 0≤t≤T, T=40ms, with sample frequency is f to itS=80KHz sampling, y (n)=A0cos(2πfcwnTS), it is right
It carries out FFT transform, it may be assumed that
The algorithm of proposition, which is realized, includes following several steps to the first range estimation of Doppler factor:
(1) CW signal initial position is determined；
(2) CW signal y (n) is extracted from received data；
(3) 2 are carried out to y (n)mSecondary FFT transform, wherein 2mFor the smallest positive integral more than or equal to y (n)；
(4) transformed Y (k) is scanned for, searches for point N corresponding to wherein amplitude maximum1, calculate respective frequencies
fmax, and comparison point N1Left and right two o'clock amplitude size show that the biggish point of amplitude is N2；
(5) according to FFT transform points N and point N1And N2Positional relationship and sample frequency fsCome determine Doppler because
Sub just range delta, such as fruit dot N2In point N1When the right, then Doppler factor just range can be obtained are as follows:
fmax/fcw-1≤Δ≤(fmax+fs/N/2)/fcw-1
As point N2In point N1When the left side, then Doppler factor just range can be obtained are as follows:
(fmax-fs/N/2)/fcw-1≤Δ≤fmax/fcw-1。
The above-mentioned first step determines that CW signal initial position is that input data packet is passed through a LFM matched filter, detection
The peak value of correlator out, peak value correspond to LFM signal deadline.
3, Doppler factor is accurately estimated
Doppler factor accurately estimate to be estimated by ambiguity function method, i.e., the LFM signal received is passed through one
The matched filter of the corresponding LFM signal of series difference Doppler factor, when the shock response and input signal of matched filter
When matching, the output signal-to-noise ratio of matched filter is maximum, and Doppler factor corresponding to this matched filter shock response must
So it is able to reflect the size of the Doppler factor of input signal.Basic principle is as follows:
1) description of ambiguity function ambiguity function is as caused by range delay and Doppler frequency shift when matched filter mismatch
Situation of change.The present invention defines the ambiguity function of broadband continuous signal from matched filter output:
When considering to receive signal r (t), we can define cross ambiguity function:
In order to estimate to receive the Doppler frequency shift of signal r (t), we are required to scan for Δ, when the τ that is delayed is 0, search mutual
Close function χsrCorresponding Δ when the maximum amplitude of (0, Δ):
Situation of change of the function description as caused by range delay and Doppler frequency shift when matched filter mismatch is pasted, in order to
Matched filter has sufficiently high Doppler factor detection performance and Time delay Estimation Accuracy, and the bandwidth that must meet LFM signal multiplies
Product BT is sufficiently large, and the noise for receiving signal is bigger.Work as BT=400, SNR=10, when delay τ is 0, cross-correlation function | χsr
(0, Δ) | as shown in Figure 2.And assume that Doppler factor is 0.01, and when passing through matched filter group, each matched filter
The maximum value of output as can be seen from Figure 3 exports maximum value 0.01.
The accurate estimation correlation method of Doppler factor is as shown in figure 4, specific implementation step is as follows:
1) determine the quantity M of matched filter, wherein the quantity M of matched filter be the Doppler according to obtained by front because
The estimated accuracy Δ of subrange Δ and Doppler factormaxIt determines, i.e. M=[(f2/fcw-f1/fcw)/Δmax], wherein []
It indicates to be more than or equal to (f2/fcw-f1/fcw)/ΔmaxSmallest positive integral, the present invention in estimated accuracy be 0.0002；
2) the LFM Signal Matching filter of M different Doppler factors is set, and the resolution ratio of matched filter group is
Δmax, the LFM signal received is passed through into matched filter group；
3) maximum value for comparing the output of M matched filter, obtains maximum value, correlator corresponding to maximum value be exactly with
The received LFM signal correlation of institute is best, to obtain accurate Doppler factor.
The implementation flow chart of entire Doppler factor estimation is as shown in Figure 5.
In addition to the implementation, the present invention can also have other embodiments, all to use equivalent substitution or equivalent transformation shape
The technical solution of formula, for example in accurate estimation, can be obtained using based on Fourier Transform of Fractional Order (FRFT), all fall within this
It invents in desired protection scope.
Claims (3)
1. a kind of underwater sound communication Doppler factor estimation method of low computation complexity, which is characterized in that this method is based on water
Sound communication system is transmitted packet structure and is realized, the method includes:
The just range estimation of step 1) Doppler factor；
Step 2) Doppler factor is accurately estimated；
The transmission packet structure is successively made of LFM signal, protection interval, CW signal, protection interval, data to be transmitted；
Step 1) the Doppler factor just range estimation is locked in Doppler factor in one small range, the specific step
Suddenly include:
1) CW signal initial position is determined by transmitting packet structure, extract subsequent CW signal；
2) frequency detecting is carried out to CW signal using traditional FFT frequency measuring method, after carrying out FFT transform, searches for wherein amplitude maximum
Corresponding point N1, calculate respective frequencies fmax, it is assumed that CW signal frequency is f when transmittingcw, available Doppler factor Δ=
fmax/fcw-1；
Due to fence effect, acquired frequency fmaxIt may be with the frequency f' of CW signal when receivingcwThere is certain deviation, so more
General Le factor Δ may have relatively large deviation with true Doppler factor；In order to avoid such case, first comparison point N1Left and right two
Point amplitude size show that the biggish point of amplitude is N2；
3) according to FFT transform points N and point N1And N2Relationship and sample frequency fsTo determine Doppler factor just range
Δ, such as fruit dot N2In point N1When the right, then Doppler factor just range can be obtained are as follows:
fmax/fcw-1≤Δ≤(fmax+fs/N/2)/fcw-1
As point N2In point N1When the left side, then Doppler factor just range can be obtained are as follows:
(fmax-fs/N/2)/fcw-1≤Δ≤fmax/fcw-1。
2. a kind of underwater sound communication Doppler factor estimation method of low computation complexity according to claim 1, feature
It is, it is described to determine that CW signal initial position specific method transmits LFM signal in data packet to use by transmitting packet structure
Matched filter to received data packet carry out matched filtering, it may be determined that CW signal initial position.
3. a kind of underwater sound communication Doppler factor estimation method of low computation complexity according to claim 1, feature
It is, the step 2) Doppler factor accurately estimate to be estimated by ambiguity function method, i.e., the LFM signal that will be received
By a series of corresponding LFM signal correlator of difference Doppler factors, when shock response and the input signal phase of correlator
The output signal-to-noise ratio of timing, correlator is maximum, and Doppler factor corresponding to this correlator shock response is necessarily able to reflect defeated
Enter the size of the Doppler factor of signal, which specifically includes:
1) the quantity M of correlator is determined, wherein the first range delta of Doppler factor obtained by the quantity M Shi Gen Ju Walk rapid 1 of correlator
With the estimated accuracy Δ of Doppler factormaxIt determines, i.e. M=[(f2/fcw-f1/fcw)/Δmax], wherein [] indicate be greater than etc.
In (f2/fcw-f1/fcw)/ΔmaxSmallest positive integral, fcwIndicate the frequency of CW signal, f1Indicate the lower limit of frequency, f2Indicate frequency
The upper limit of rate；
2) the corresponding LFM signal correlator of M difference Doppler factor is set, and the resolution ratio of correlator group is Δmax, will receive
The LFM signal arrived passes through correlator group；
3) maximum value for comparing the output of M correlator, obtains maximum value, and correlator corresponding to maximum value is exactly received with institute
LFM signal correlation is best, to obtain accurate Doppler factor.
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| CN112118201B (en) * | 2018-01-11 | 2023-03-07 | 福建星海通信科技有限公司 | LFM-based combined Doppler estimation method |
| CN108924073B (en) * | 2018-06-28 | 2019-08-20 | 中国科学院声学研究所 | A kind of quick self-adapted Doppler estimation synchronous based on pseudo-random sequence |
| CN112787730A (en) * | 2020-12-25 | 2021-05-11 | 青岛三海科技有限公司 | Doppler estimation method based on joint waveform design |
| CN112887240B (en) * | 2021-03-12 | 2022-04-19 | 哈尔滨工程大学 | Doppler factor estimation method based on dual Kalman filtering |
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